This invention relates to the art of motion converting mechanisms, and more particularly to mechanisms for converting axial movement into rotational movement. Specifically, the present invention relates to a rotator mechanism for use in rotating a valve of an internal combustion engine and will be particularly described with reference thereto.
Rotators for rotating valves of an internal combustion engine are known. Such valve rotators include first and second parts which are mounted for movement relative to one another axially and rotatably along and about a longitudinal axis. One part has pockets in which balls are positioned for imparting relative rotation to the parts in response to relative axial movement of the parts. The pockets define a predetermined path along which the balls move. Specifically, the balls move along an inclined ramp which forms the bottom of the pocket. Numerous patents and other publications disclose rotators such as noted above and typical of such are U.S. Pat. Nos. 3,710,768 and 3,890,943.
In such rotators, the ramp along which the ball moves extends at a single angle to a plane extending perpendicular to the longitudinal axis of the valve, which axis is also the axis about which relative rotation occurs of the first and second parts of the rotator. The magnitude of the single ramp angle is determined usually as a compromise based on design consideration. A shallow single ramp angle provides for a greater load capacity and greater rotational movement of the valve for a given amount of axial movement of the balls as measured along the longitudinal axis of the valve stem. A steep single ramp angle allows the balls to roll more easily but less load capacity and rotational movement are provided for a given amount of axial movement of the balls as measured along the longitudinal axis of the valve stem.
In the single ramp angle designs the axial force which is required to move the ball from its starting position down the ramp for a given amount of axial movement of the ball remains the same throughout the extent of action of the rotator. Further, the amount of angular rotation for a given amount of axial ball movement also remains the same during the action of the rotator. Also, the single ramp angle rotators have suffered from sliding action between the ball and its contacting surfaces, and of course, any sliding reduces the life of the rotator.
The present invention is directed to a rotator design which enables greater efficiency and durability to be achieved and also provides the advantages of design flexibility as compared to the single ramp angle design.
The present invention specifically provides for a valve rotator of the above-noted construction where the ramp along which a ball moves is formed at plural angles. Specifically, the ramp along which the ball moves is formed of a plurality of surface portions which extend at different angles to a plane extending perpendicular to the longitudinal axis of the valve. A surface portion adjacent the end of the ramp at which the ball is located prior to axial movement of the parts of the rotator toward each other is at the greatest angle to the plane which extends perpendicular to the longitudinal axis of the valve. The angle at which the other surface portions of the ramp extend to the plane perpendicular to the longitudinal axis of the valve becomes progressively less as the ramp progresses toward the other end thereof. In other words, the order of angles used in a particular pocket is from steep to shallow as the ball rolls down the ramp.
As a result of this construction and due to the fact that the steeper angle is located at the end of the ramp where the ball begins its action, less vertical force on the ball is required to start the rolling motion of the ball. Increased rolling of the ball produces increased rotation and less sliding of the ball relative its adjacent surfaces. As a result, due to the fact that less sliding between the ball and its contacting surfaces occurs, the life of the device of the present invention is improved.
Further, the present invention provides a substantial advantage in increased design flexibility. Because of the multiple angle raceway ramp, a more precise rotator design can be effected for a given application. Specifically, because of the multiple ramp angle design, the vertical force required to move the ball down the ramp for an amount of axial ball movement will increase with each decrease in ramp angle and further the amount of angular rotation of the valve for an amount of axial ball movement will increase with each change in ramp angle.
U.S. Pat. No. 2,875,740 was uncovered as a result of a patentability study and search relative to the subject disclosure. The U.S. Pat. No. 2,875,740 does not operate on the principle of the subject disclosure. This patent is a lash adjuster rather than a rotator. Further, the balls in this patent are not constrained to move in a particular predetermined path defined by surfaces of a pocket in which the balls are located in accordance with the present invention.